Fouling of surfaces exposed to an aquatic environment is a serious problem. For example, surfaces of ships such as the hull, offshore marine structures such as oil rigs, sea water conduit systems for seaside plants, buoys, heat-exchangers, cooling towers, de-salination equipment, filtration membranes, docks, and the like may all experience some degree of fouling when continually exposed to water. In the case of ships, fouling can inhibit vessel performance and capabilities. For example, fouling may substantially increase fuel consumption and may necessitate extensive and more frequent maintenance, all of which raise the overall costs of operation. Fouling may also reduce ship speed, maneuverability, and range, which impede performance. On another level, attachment of regionally specific aquatic organisms on ships that traverse the world can lead to the unwanted invasion and infestation of these organisms to non-indigenous harbors. In some instances, this can have severe adverse effects on local aquatic ecosystems.
Over the years there have been numerous attempts to minimize the effect of fouling on structures exposed to an aquatic environment. For example, coatings (e.g., paints, etc.) have been developed that impede the attachment and/or growth of aquatic organisms on such structures. Traditionally, two parallel lines of coatings research have predominated: biocide containing coatings and low surface energy, “non-stick,” fouling release coatings.
The most common approach to control marine fouling on the hulls of ships involves dispersing copper oxide particles in a degradable polymer matrix to produce an antifouling coating. The copper oxide serves as a biocide that deters settlement of marine organisms. Since the copper oxide is not chemically bound to the polymer matrix, it is gradually removed from the coating surface. The slow degradation of the polymer matrix in an aqueous environment allows for replenishment of the coating surface with copper oxide to maintain biocidal activity. After about three years of service, the degree of degradation of the coating is severe enough that the ship must be dry docked and a fresh layer of coating applied. While this approach is effective, it is undesirable due to release of copper oxide into the marine environment and the need for frequent dry docking.
The second approach, which is currently being used to a much lesser degree, involves the application of a nontoxic, non degradable coating that allows for easy release of marine organisms that have settled on the coating. These coatings, commonly referred to as foul-release coatings, are typically silicone elastomers that possess a low surface energy such that the adhesion strength is relatively low and organisms can be readily removed by water jetting or moving the ship at high speed through the water. The primary disadvantage of this approach is that frequent cleaning of ship hulls is required and the coatings are easily damaged due to their low modulus.
Accordingly, it would be desirable to provide an improved antifouling coating (i.e., a coating having biocidal properties and/or foul-release properties) that is more environmentally sensitive and/or is more effective at inhibiting fouling.